The flow rates of conventional drippers and PC drippers are much higher than the required flow rates for meeting plants' water requirements. This is what makes drip irrigation systems complicated and expensive, and this is why drip irrigation systems are usually designed to operate in several sets using many automatic valves, irrigation computers, etc.
Water that flows from a single conventional dripper to the ground forms an onion-shaped wetted volume of soil. In light soils, the onion shape looks more like a long and narrow cylinder. Such long and narrow onion shapes waste substantial amounts of water and fertilizers by deep percolation.
As known, soils have limited capacity to store water. When water is applied in large quantities in each irrigation cycle, excess water is wasted by flowing below the plants' root zones.
Most plants develop much faster when the soil is kept continually at high humidity and at low water tension, while at the same time the soil is well-aerated.
When, e.g., a nursery includes 100,000 potted plants, in order to simultaneously irrigate the 100,000 plants using conventional PC drippers each operating at a flow of 1 l/hr, a total flow of 100,000 l/hr is required. If, instead, each dripper is operated at a PC flow of 0.1 l/hr, a total flow rate of only 10,000 l/hr is required for simultaneously operating the irrigation system.
PC drippers that operate at a low flow rate of lower than 0.5 l/hr, are not available in the market, because they are highly susceptible to plugging.
For different applications and for solving some of the above-described problems, there is a need for PC drippers that operate at relatively lower flows.
Therefore, the present invention relates to an apparatus and method for operating NCPC drippers at very low flow rates, for example, to flow rates of only 0.1 l/hr, or lower.
In accordance with the present invention there is therefore provided an apparatus for operating a group of normally closed, pressure compensated drippers at relatively low liquid flow rates, comprising a pulsating device having an inlet and an outlet that converts a low continuous liquid flow rate entering its inlet, through a flow control unit, to a high intermittent and pulsating flow rate ejected through its outlet, a manifold having an inlet connected to the outlet of said pulsating device, a group of normally-closed, pressure-compensated drippers connected to said manifold, wherein said pulsating device converts a low continuous flow rate of liquid entering its inlet, through the flow control unit, to a high intermittent and pulsating flow rate that ejects from its outlet and flows from its outlet through the inlet of said manifold and through said normally-closed, pressure-compensated group of drippers connected to said manifold, out from said drippers, at a pressure-compensated low flow rate.
The invention further provides a method of operating pressure-compensated drippers at low liquid flow rates, comprising providing one or more drip-lines, each drip-line including a first closed end and a second end, and a plurality of normally-closed, pressure-compensated drippers, connecting said second end to a pulsating device converting a low continuous flow rate of liquid entering the drip-line into a high, intermittent and pulsating flow of liquid, thereby liquid of high intermittent and pulsating flow is ejected from at least part of said normally-closed, pressure-compensated drippers.
The apparatus consists of a group of NCPC drippers connected, as will be described hereinafter, to the outlet of a pulsating device. Such NC drippers and pulsating devices are commonly available on the market, e.g., pulsators of the type described in the U.S. Pat. No. 5,507,436.
The pulsating device utilized in the present invention converts a low, continuous, controlled, relatively low flow rate entering its inlet to a high, intermittent, and pulsating flow ejected through its outlet. For example, by connecting a 2 l/hr flow control unit to the inlet of such a pulsating device, the pulsating device will convert the flow rate of the 2 l/hr dripper entering its inlet, to a high instant and pulsating flow rate of, e.g., 40 l/hr. By connecting a group of, e.g., 20 NCPC drippers, each of which operates at a nominal flow rate of 2 l/hr, to the outlet of such a pulsating device, each dripper in the group will operate at a flow rate of only 0.1 l/hr, and it will be PC.
In the previous example, each PC dripper in the group will operate at the same flow regardless of its elevation or the pressure at its inlet. Also the group of, e.g., 20 drippers are commercial NCPC drippers of 2 l/hr each, which are relatively less sensitive to plugging problems, yet each of them operates at a relatively low flow rate of only 0.1 l/hr.
The present invention relates to NCPC drippers, which drippers open themselves at a pre-set pressure. For example, the NCPC drippers will remain closed when the pressure at their inlet is lower than a pre-set pressure of, e.g., 0.3 bars. In such a case, at any pressure lower than 0.3 bars, the drippers will remain closed and no liquid will flow from their inlet through their outlet. In this example, liquid will flow through the outlet of the drippers only when the pressure at their inlet will be higher than 0.3 bars.
By changing the flow of the flow control unit at the inlet to the pulsating device, the flow of all the drippers in the group will change accordingly. For example, when a 4 l/hr unit at the inlet of a pulsating device controls the flow rate of a group of 100 NCPC 2 l/hr drippers, the flow rate of liquid through each dripper in the group will be 0.04 l/hr. By changing the unit at the inlet to the pulsating device from a 4 l/hr dripper to an 8 l/hr unit, the flow rate of each dripper in the group will change from 0.04 l/hr to 0.08 l/hr.